Place an opened bag of M&M's into an airtight container or freezer bag. 

If available, use aluminum foil to wrap the opened packet tightly. 

Slide the foil packet into a freezer-safe zipper bag. 

Remove as much air as possible when using a freezer-safe bag. 

Seal the bag.

Then label it with the current date. If it isn’t already, make sure it’s at room temperature before moving to the freezer.